Ultrasonic search unit with rolling contact

ABSTRACT

An ultrasonic wheel search unit for testing elongated bodies wherein a fluid impervious, flexible, ultrasonically transparent diaphragm defines a fluid-filled wheel chamber and a separate fluid-filled transducer chamber, enabling rapid transducer change. Means are provided to vary the relative pressure between dissimilar fluids in the two chambers to vary the beam pattern of the search unit.

United stat;

White [54] ULTRASONIC SEARCH UNIT WITH ROLLING CONTACT [72] Inventor:Allwyn M. White, Danbury, Conn.

[73] Assignee: Automation Industries, Inc., Century City,

Calif.

[22] Filed: Sept. 11, 1969 [21] Appl. No.: 57,104

[52] U.S. Cl ..73/7l.5, 73/67.85

[51] Int. Cl. ..G01n 29/00 [58] Field ofSearch ..73/67.5-67.9, 71.5;310/83 [56] References Cited UNITED STATES PATENTS 2,545,101 3/1951Mevnier 3,168,659 2/1965 Bayre et a1 3,205,702 9/1965 Joy u ..,73 /'1 5Primary Examiner-Richard C. Queisser Assistant Examiner-Arthur E.Korkosz AttorneyDan R. Sadler [5 7] ABSTRACT An ultrasonic wheel searchunit for testing elongated bodies wherein a fluid impervious, flexible,ultrasonically transparent diaphragm defines a fluid-filled wheelchamber and a separate fluid-filled transducer chamber, enabling rapidtransducer change. Means are provided to vary the relative pressurebetween dissimilar fluids in the two chambers to vary the beam patternof the search unit.

12 Claims, 4 Drawing Figures PATENTED JANZSIHYZ $53 SHEET 1 BF 2 Fig. 5.

1 Receiver Amplifier Transmitter Synch. Sweep Allwyn M. White,

INVENTOR.

ATTORNEY.

PATENTED JAN25 I972 SHEET 2 BF 2 Fig 2.

Allwyn M. White,

INVENTOR.

@ TRSML ATTORNEY.

ULTRASONIC SEARCH UNIT-WITH ROLLING CONTACT BACKGROUND OF THEINVENTION 1. Field of Invention The present invention relates to anultrasonic search unit and more particularly to a wheel-type search unitproviding a rolling coupling to test elongated material having meansenabling rapid transducer replacement and enabling variation of thetransducer beam pattern.

2. Description of Prior Art At the present time it is frequentlydesirable to transmit ultrasonic energy into a material for inspecting,testing and/or measuring the material. One means of accomplishing thisis to employ a transducer having a mechanically vibratable member whichmay be interconnected with a source of electrical signals such as anoscillator that operates in the ultrasonic region. The transducer willthereby radiate ultrasonic energy. If the transducer is acousticallycoupled to a test specimen the radiated ultrasonic energy will bedirected into the specimen. By observing the manner in which thisultrasonic energy travels through the specimen and/or is internallyreflected, various characteristics such as the presence of internalflaws, dimensions, etc., may be detemiined.

Normally, the mechanically vibratable member in the transducer is apiezoelectric member such as a quartz crystal or a piezoelectric ceramicmaterial, having a radiating surface which mechanically vibrates when asuitable electrical signal is applied thereto. The mechanical vibrationsof the radiating surface cause corresponding vibrations to be coupledinto the surrounding medium so as to travel therethrough as a beam ofultrasonic energy.

During testing the ultrasonic transducer must, of course, be coupled tothe test material or workpiece. When the workpiece is itself moving, theultrasonic transducer must be coupled to the material in a fashion whichis compatible with the movement. For applications such as themeasurement or testing of tubes and bars in production, transducer unitshave been developed which use rotating members to couple longitudinalwaves into and out of the workpieces. One such prior art wheel-typesearch unit has a rolling coupler which may be generally described as ahollow wheel having an ultrasonically transparent tire inflated with aliquid. A piezoelectric crystal, or other generator of longitudinalultrasonic waves, is immersed within the liquid in the wheel and, uponexcitation of the generator, ultrasonic waves are transmitted radiallyoutwardly through the fluid couplant to the surface of the tire, andafter passing through the tire, are coupled to the workpiece.

The pattern of the beam and the manner in which the energy isdistributed within the beam is determined by a wide variety of factorssuch as the size and shape of the surface of the crystal, the frequencyof the energy and the distance from the crystal. Heretofore, the energyfrom a transducer in a wheel-type search unit has been radiated in apredetermined fixed pattern that could not be readily varied. Althoughthe radiation pattern for any given transducer may be particularly wellsuited for certain types of observations, it may not be well suited forother types of observations. For example, if the transducer radiates abroad beam it is extremely difficult, if not impossible, to detect smallinternal flaws, particularly those flaws located within the near fieldregion. Conversely, if the transducer radiates a very narrow beam it isextremely difficult, if not impossible, to rapidly search large areas.As a consequence, it has been necessary to select a transducer thatradiates a beam especially adapted to the particular operation beingperformed. If the operation to be performed is changed, it has beennecessary to replace the transducer employed in the search unit withanother more suitable type.

Replacing the transducer in wheel-type search units has heretofore beena difficult, time consuming task. The search unit must be demounted andthe wheel laid on its side. The pressure maintained in the search unitto enable coupling ultrasonic energy through the tire to the workpieceis released as the transducer is removed and another is inserted. Thisresults in a loss of coupling fluid, introducing air bubbles into theinterior of the tire. Since such bubbles cause spurious responses andgreatly attenuate transmitted and received ultrasonic energy traversingthe wheel, great pains must be taken to remove all bubbles from thesearch unit before rescaling.

SUMMARY OF THE INVENTION In the present invention the ultrasonictransducer is mounted in a chamber separated from the fluid-containingchamber including the rotating wheel by a flexible diaphragm which istransparent to ultrasonic energy. When replacing the transducer, thefluid under pressure contained in the chamber including the rotatingwheel need not be disturbed. The transducer may then be readily removedand replaced without introducing bubbles of air. A coupling fluid isprovided in the chamber including the transducer and separated by thediaphragm from the rotating wheel. The coupling fluid in the transducerchamber may have different ultrasonic properties from that containedwithin the rotating wheel chamber. Means are provided for varying thepressure of the fluid in the transducer chamber, enabling variabledeflection of the diaphragm separating the transducer chamber from thewheel. Deflection of the diaphragm, separating fluids having differingultrasonic properties, such as velocity of propagation, enablesvariation of the beam shape produced by the transducer. Such variationin beam shape enables greater versatility of use of a given transducer,reducing the need for changing transducers.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified block diagramillustrating an ultrasonic test system employing the wheel search unitof the present invention;

FIG. 2 is a cross-sectional view of the wheel search unit;

FIG. 3 is a section taken along line 33 of FIG. 2; and

FIG. 4 is an end view of the search unit of FIG. 2.

DESCRIFT ION OF THE PREFERRED EMBODIMENT A simplified schematic diagramof an ultrasonic testing system 10 is illustrated in FIG. 1. Anultrasonic wheel search unit 12 is provided having a wheel adapted torotate to accommodate rapid relative movement of a workpiece 14 withrespect to the search unit 12. The search unit 12 includes an ultrasonictransducer connected to a pulse transmitter 16. The pulse repetitionrate of transmitter 16 is controlled by synchronizing pulse generator18. Also controlled by synchronizing pulse generator 18 is sweepgenerator 20, connected to the horizontal deflection plates ofcathode-ray oscil loscope 22. Ultrasonic pulses generated by thetransducer in response to electrical pulses from transmitter 16 arelaunched into workpiece 14. The ultrasonic pulses are reflected by flawswhich may be present in the workpiece 14. The reflected ultrasonicpulses are receivedby the search unit and converted back into ultrasonicfrequency electrical signals by the transducer. The ultrasonic frequencysignals are applied to a receiver 24, wherein they are converted intovideo signals. Video signals from receiver 24 are amplified by asuitable video amplifier 26 and applied to the vertical deflectionplates of cathodeqay oscilloscope 22. Sweep generator 20 provides thehorizontal sweep triggered by synchronizing pulse generator 18simultaneously with the transmitted pulse. The video signals deflect thehorizontal sweep vertically at a time dependent upon the depth of theflaw in workpiece l4 reflecting the ultrasonic pulses. The horizontalsweep may be calibrated to read depth directly.

The ultrasonic wheel search unit 12 of the present invention includes afixed hub assembly 28 and a rotating wheel assembly 30 rotating abouthub assembly 28. Wheel assembly 30 is mounted on rear ball bearing 32and front ball bearing 34 which are secured to hub assembly 28, enablingrotation of wheel assembly 30 about hub assembly 28. Tire clamp 36,

removably secured torearwheel housing 38, seals the ultrasonicallytransparent tire 42 to wheel housing 38. The second rim 44 of tire 42 issecured to front wheel housing46 by a removably mounted clamp and valveassembly 48. A circular sealing member 50 is mounted on rear wheelhousing 38. Sealing member 50-is provided with a lip bearing against thecircumference of hub assembly 28 to prevent leakage of coupling fluidfrom the interior of wheel assembly 30 through the rear ball bearing 32.

In contrast to the provision of seal 50 to prevent leakage through therear ball bearing 32, no attempt is made to keep the coupling fluid outof front ball bearing 34. Front ball bearing 34 is of a type adapted tooperate immersed in the coupling fluid such as distilled water,contained within wheel assembly 30.

Hub assembly 28 is conveniently fabricated in three portions which arethreaded together as illustrated in FIG. 2. A flexible diaphragm 52,transparent to ultrasonic energy, is mounted between the two threadedportions of hub assembly 28. Diaphragm 52 serves to divide search unit12 into two separate fluidtight chambers, each adapted to be filled withcoupling fluid separately and individually. The two fluids may differ incomposition, and have different pressures.

A cylindrical piezoelectric ultrasonic transducer 54 is removablymounted in the hollow cylindrical interior of hub assembly 28. As iswell known to those skilled in the art, the transducer 54 is providedwith an active piezoelectric surface 56 at the end of the cylindricalbody, adapted to direct a beam of ultrasonic energy through diaphragm52. A planar reflector 58 having a reflecting surface at substantially a45 angle to theplane of the active surface 56 of transducer 54, isprovided to change the path of the beam of ultrasonic energy, reflectingthe beam through an angle of 90', directing the beam downwardly throughthe bottom of tire 42, adapted for con? tact with workpiece 14.

The transducer 54' is provided with a flange60 abutting against shoulder62 on hub assembly 28. An O-ring seal 64 on transducer 54 adjacentflange 60 cooperates with shoulder 62 to seal the coupling fluid-filledtransducer chamber, thereby preventing leakage of coupling fluid aboutflange 60. A hollow threaded nut 66 engages with the threads provided onthe interior of hub assembly 28, bearing against flange 60 to compress'O-ring seal 64 against shoulder 62. The hollow interior of nut 66enables access to electrical connector 68, providing for connection oftransducer 54 into circuit with transmitter 16 andrec eiver 24 throughan electrical conductor, such as a coaxial cable 70.

As disclosed hereinabove, diaphragm 52 divides wheel search unit 12 intotwo separate fluidtight compartments. Each compartment is provided withfilling means for filling the compartment with a suitable ultrasoniccoupling fluid. The wheel compartment is provided with a wheel couplingfluidfilling valve 72 and the transducer compartment is provided with atransducer compartment coupling fluid-filling valve 74.

' A circular channel 73 and longitudinal groove 75 distribute thecoupling fluid from filling valve 74 about the periphery of thetransducer 54, and into the space between active surface 56 anddiaphragm 52.

3 Since gasses are substantially opaque to ultrasonic energy, means mustbe provided to eliminate from the compartments any gas bubbles remainingafter filling the compartments with coupling fluid through filling valve72. A bleed valve 76 is provided in the wheel compartment to enablebleeding out gas bubbles remaining in the wheel compartment. Bleed valve76 is open during the filling operation until all gas bubbles areexpelled. Bleed valve 76 may then be closed. Coupling fluid may continueto be forced into the wheel compartment filling valve 72 until thedesired pressure is reached. Filling valve 72 may then be closed,sealing the wheel compartment. The wheel compartment now need not bedisturbed when it is desired to change the transducer. Refilling isnecessary only in case of a leak due to an accident.

T he, transducer compartment may conveniently be filled through thehollow cylindrical interior of hub assembly 28. Transducer 54 is theninserted into the cylindrical interior of hub assembly 28, forcingexcess fluid out about the flange 60. Nut 66 is screwed into the hubassembly, compressing O-ring seal 64. Additional fluid'may beadded ifnecessary through transducer compartment filling valve 74. Any gasbubbles present in the transducer compartment may be bled off throughbleed valve 78. Reasonable care while replacing a transducer preventsinclusion of any bubbles, however. Upon reaching the desired nominalpressure within the transducer compartment, filling valve 74 may beclosedv Means are provided whereby the relative pressures in the wheelcompartment and transducer compartment may be varied to vary theposition of diaphragm 52. The employment of coupling fluids havingdiffering ultrasonic propagation characteristics enables the beampattern to be varied by varying the configuration of diaphragm 52defining the interface between the two different coupling fluids.Exemplarily, the wheel compartment may be filled with distilled waterand the transducer compartment may be filled with glycerin. By varyingthe relative pressures in the two compartments, diaphragm 52 may becaused to assume a convex shape bulging toward reflector 58, or may becaused to assume a concave configuration facing reflector 58.

A cylinder 82 communicating with the transducer coupling fluidcompartment is provided with an adjustable piston 80. Fluidtightness ismaintained between piston 80 and the walls of cylinder 82 by means of anO-ring seal 84 mounted in a groove about the circumference of piston 80;Piston 80 is provided with an externally threaded portion 86 cooperatingwith an internally threaded insert 88 secured to hub assembly 28. Agroove 90 is provided for screwdriver adjustment of the position ofpiston 80. As piston 80 is advanced into cylinder 82, the pressure inthe transducer chamber is increased, forcing diaphragm 52 to bulgeoutwardly toward reflector 58. Conversely, withdrawing piston 80upwardly in cylinder 82 lowers the pressure in the transducer chamberand diaphragm 52 is bowed inwardly toward active face 56 of transducer54 by the relatively greater, pressure in the wheel compartment.

As disclosed hereinabove coupling fluids having differing propagationcharacteristics are present in the two compartments. The shape ofdiaphragm 52 defines the shape of the interface between the fluids inthe two compartments. When diaphragm 52 is caused to bulge towardtransducer 54 by lowering the pressure, a concave lens is formed. Thebeam of ultrasonic energy propagated between active face 56 of trans-'ducer 54 is caused to diverge by the concave lens resulting in arelatively wide beam pattern. Conversely, when the diaphragm 52 iscaused to bulge convexly toward reflector 58 a convex lens is formed.The beam of ultrasonic energy from transducer 54 becomes convergent,resulting in a coverage of a smaller area of the workpiece. Obviouslywhen the pressures are adjusted to be equal, diaphragm 52 remains planarand there is no effect upon the shape of the beam of ultrasonic energytransmitted by the transducer.

The wheel search unit assembly of the present invention is normallyfixedly mounted adjacent the path of the workpiece.

It is usually desirable to have the beam of ultrasonic energy enter theworkpiece perpendicularly to the surface thereof. Means are provided,therefore, to enable rotation of the hub assembly with respect to themounting bracket portion of hub assembly 28. A split ring clamp 92 isadapted to be tightened and secured by a machine screw 94. Hub adjustingscrews may be loosened to enable relative rotation of hub assembly 28with respect to the mounting fixture. At the optimum position thelocknuts on adjusting screws are secured thus locking the position ofhub assembly 28.

The wheel search unit disclosed hereinabove enables quick and simplereplacement of transducer units without requiring disassembly andtime-consuming refilling of the search unit. Further, means are providedfor varying the pattern of the ultrasonic beam provided by thetransducer installed in the search unit. By a simple screwdriveradjustment, the beam of ultrasonic energy from a given transducer may becaused to become divergent or convergent as required.

Iclaim: 1. In combination with an instrument for ultrasonicallyinspecting a workpiece:

a fixed hub including a hollow interior; a spindle separably mounted tosaid fixed hub and including a hollow interior aligned with the hollowinterior of said fixed hub, said spindle including an opening disposedperpendicular to the axis of said spindle leading from the ho]- lowinterior thereof; a first chamber being defined in the hollow interiorof said hub; a second chamber being defined in the hollow interior ofsaid spindle; an ultrasonic transparent separating wall mounted in theinterior of saim'ridl seiparating said first chamber from said secondchamber; an ultrasonic transducer disposed in said second chamber, saidtransducer having a beam emitting surface disposed parallel to thesurface of said separating wall; a Wheel sssmhlxrstatahly.mounted.Qnsaidp e an u fiasonic transparent tire mounted on said wheel assemblyincluding iiiterior area said tire being adapted to be in rollingcontact with the workpiece; fluid coupling means disposed in said firstchamber and second chamber; reflector means disposed in said firstchamber for directing ultrasonic beams from the beam emitting surface ofsaid transducer towards the opening in said spindle and to the entrantsurface of said workpiece; and means mountedv in said hub andcommunicated with said second charnberjgg changigg t l g rgla t iyg i l?P YQEH 91. .flt tchamberandsecon whereby said wheel assembly and saidtire roll across the surface of said workpiece during a test and serveto transmit ultrasonic energy to and from said workpiece and whereby thepath of ultrasonic energy is from the beam emitting surface of saidtransducer through the ultrasonically transparent separating wall,reflected from said reflector means and into said workpiece. 2. Incombination: a container including a first chamber and a second chamber,each chamber being separably coupled to the other, said containerincluding a rotatable contacting surface mounted to the second chamber,and a transducer whereby the path of ultrasonic energy is from the beamemitting surface of said transducer through said flexible diaphragm intosaid workpiece.

3. The combination defined in claim 2 and including beam deflectingmeans mounted in the second chamber of said container for deflecting thebeam of said transducer towards said contacting surface.

4. An ultrasonic search unit including:

a spindle mounted to said hub;

a first chamber and a second chamber defined in said fixed hub and saidspindle, said first chamber and said second I chamber beingsubstantially aligned with each other;

an ultrasonic transparent separating wall mounted to said first chamberto separate said first chamber and second chamber;

a ultrasonic transducer disposed in said second chamber;

access means in said second chamber for gaining access into said secondchamber for allowing access to said transducer therein;

a wheel assembly rotatably mounted on said spindle;

an ultrasonic transparent tire on said wheel assembly including aninterior area in fluid communication with said first chamber; and

fluid coupling means disposed in said first chamber and said secondchamber;

whereby said wheel assembly and said tire roll across a surface of aworkpiece during a test and serve to transmit ultrasonic energy to andfrom said workpiece and whereby the path of said transmitted ultrasonicenergy is from said transducer through said separating wall and intosaid workpiece.

5. The search unit as defined in claim 4 and including reflector meansin said second chamber for reflecting ultrasonic energy from saidtransducer at a substantially 45 angle.

6. The search unit as defined in claim 4 wherein said separating wallbeing a flexible diaphragm.

7. The search unit as defined in claim 6 and further including means forchanging the relative pressure of the coupling fluid between said firstchamber and said second chamber.

8. The search unit as defined in claim 6 and including reflector meansin said second chamber for reflecting ultrasonic energy from saidtransducer at a substantially 45 angle.

9. in combination:

a container including a first chamber and a second chamber, each chamberbeing separably coupled to the other;

a separating wall mounted to the first chamber in said containerseparating said first chamber and said second chamber and sealing saidfirst chamber;

fluid means disposed in said container filling said first chamber andsaid second chamber;

a wheel assembly rotatably mounted on said container and including atire having an interior in fluid communication with the first chamber;and

a transducer disposed in the second chamber of said container;

whereby the tire and wheel assembly roll across a surface of a workpieceand serve to transmit ultrasonic energy from said transducer throughsaid separating wall and said fluid means and into said workpiece.

10. in the combination of claim 9 wherein said separating wall being aflexible diaphragm.

11. In the combination as defined in claim 10 and including means forchanging the relative pressures of said fluid means between said firstchamber and said second chamber.

12. in combination an ultrasonic search unit with an instrument forultrasonically inspecting a workpiece;

a fixed hub including a hollow interior;

a spindle separably mounted to said fixed hub and including a hollowinterior aligned with the hollow interior of said fixed hub, saidspindle including an opening disposed perpendicular to the axis of saidspindle leading from the hollow interior thereof;

a first chamber being defined in the hollow interior of said hub;

a second chamber being defined in the hollow interior of said spindle;

an ultrasonically transparent separating wall mounted in the interior ofsaid spindle separating said first chamber from said second chamber;

an ultrasonic transducer disposed in said second chamber, saidtransducer having a beam emitting surface disposed parallel to thesurface of said separating wall;

a wheel assembly rotatably mounted on said spindle;

transducer towards the opening in said spindle through said separatingwall and to the entrant surface of said workpiece;

a cylinder in said hub portion communicating with said second chamber;

an adjustable piston disposed in said cylinder; and

means for adjusting the relative position of said piston in saidcylinder.

1. In combination with an instrument for ultrasonically inspecting aworkpiece: a fixed hub including a hollow interior; a spindle separablymounted to said fixed hub and including a hollow interior aligned withthe hollow interior of said fixed hub, said spindle including an openingdisposed perpendicular to the axis of said spindle leading from thehollow interior thereof; a first chamber being defined in the hollowinterior of said hub; a second chamber being defined in the hollowinterior of said spindle; an ultrasonic transparent separating wallmounted in the interior of said spindle separating said first chamberfrom said second chamber; an ultrasonic transducer disposed in saidsecond chamber, said transducer having a beam emitting surface disposedparallel to the surface of said separating wall; a wheel assemblyrotatably mounted on said spindle; an ultrasonic transparent tiremounted on said wheel assembly including an interior area said tirebeing adapted to be in rolling contact with the workpiece; fluidcoupling means disposed in said first chamber and second chamber;reflector means disposed in said first chamber for directing ultrasonicbeams from the beam emitting surface of said transducer towards theopening in said spindle and to the entrant surface of said workpiece;and means mounted in said hub and communicated with said second chamberfor changing the relative pressures of fluid between said first chamberand second chamber; whereby said wheel assembly and said tire rollacross the surface of said workpiece during a test and serve to transmitultrasonic energy to and from said workpiece and whereby the path ofultrasonic energy is from the beam emitting surface of said transducerthrough the ultrasonically transparent separating wall, reflected fromsaid reflector means and into said workpiece.
 2. In combination: acontainer including a first chamber and a second chamber, each chamberbeing separably coupled to the other, said container including arotatable contacting surface mounted to the second chamber, and atransducer unit disposed in the first chamber in said container, saidtraNsducer having a beam emitting surface disposed parallel with saiddiaphragm; a flexible diaphragm mounted in said container separating thefirst and second chamber of said container; fluid means disposed in saidcontainer filling said first chamber and said second chamber thereof;and means for changing the relative pressure of the fluid means betweenthe first chamber and the second chamber of said container; whereby therotatable contacting surface of said container rolls across a workpieceduring a test and serves to transmit ultrasonic energy to and from saidworkpiece and whereby the path of ultrasonic energy is from the beamemitting surface of said transducer through said flexible diaphragm intosaid workpiece.
 3. The combination defined in claim 2 and including beamdeflecting means mounted in the second chamber of said container fordeflecting the beam of said transducer towards said contacting surface.4. An ultrasonic search unit including: a fixed hub; a spindle mountedto said hub; a first chamber and a second chamber defined in said fixedhub and said spindle, said first chamber and said second chamber beingsubstantially aligned with each other; an ultrasonic transparentseparating wall mounted to said first chamber to separate said firstchamber and second chamber; a ultrasonic transducer disposed in saidsecond chamber; access means in said second chamber for gaining accessinto said second chamber for allowing access to said transducer therein;a wheel assembly rotatably mounted on said spindle; an ultrasonictransparent tire on said wheel assembly including an interior area influid communication with said first chamber; and fluid coupling meansdisposed in said first chamber and said second chamber; whereby saidwheel assembly and said tire roll across a surface of a workpiece duringa test and serve to transmit ultrasonic energy to and from saidworkpiece and whereby the path of said transmitted ultrasonic energy isfrom said transducer through said separating wall and into saidworkpiece.
 5. The search unit as defined in claim 4 and includingreflector means in said second chamber for reflecting ultrasonic energyfrom said transducer at a substantially 45* angle.
 6. The search unit asdefined in claim 4 wherein said separating wall being a flexiblediaphragm.
 7. The search unit as defined in claim 6 and furtherincluding means for changing the relative pressure of the coupling fluidbetween said first chamber and said second chamber.
 8. The search unitas defined in claim 6 and including reflector means in said secondchamber for reflecting ultrasonic energy from said transducer at asubstantially 45* angle.
 9. In combination: a container including afirst chamber and a second chamber, each chamber being separably coupledto the other; a separating wall mounted to the first chamber in saidcontainer separating said first chamber and said second chamber andsealing said first chamber; fluid means disposed in said containerfilling said first chamber and said second chamber; a wheel assemblyrotatably mounted on said container and including a tire having aninterior in fluid communication with the first chamber; and a transducerdisposed in the second chamber of said container; whereby the tire andwheel assembly roll across a surface of a workpiece and serve totransmit ultrasonic energy from said transducer through said separatingwall and said fluid means and into said workpiece.
 10. In thecombination of claim 9 wherein said separating wall being a flexiblediaphragm.
 11. In the combination as defined in claim 10 and includingmeans for changing the relative pressures of said fluid means betweensaid first chamber and said second chamber.
 12. In combination anultrasonic search unit with an instrument for ultrasonically inspectinga workpiece; a fixed hub including a hollow interior; A spindleseparably mounted to said fixed hub and including a hollow interioraligned with the hollow interior of said fixed hub, said spindleincluding an opening disposed perpendicular to the axis of said spindleleading from the hollow interior thereof; a first chamber being definedin the hollow interior of said hub; a second chamber being defined inthe hollow interior of said spindle; an ultrasonically transparentseparating wall mounted in the interior of said spindle separating saidfirst chamber from said second chamber; an ultrasonic transducerdisposed in said second chamber, said transducer having a beam emittingsurface disposed parallel to the surface of said separating wall; awheel assembly rotatably mounted on said spindle; an ultrasonicallytransparent tire mounted on said wheel assembly including an interiorarea, said tire being adapted to be in rolling contact with theworkpiece; a first fluid coupling means disposed in said first chamber;a second fluid coupling means being disposed in said second chamber saidfirst fluid coupling means and said second fluid coupling means havingdifferent acoustic impedances; reflector means disposed in said firstchamber for directing ultrasonic beams from the beam emitting surface ofsaid transducer towards the opening in said spindle through saidseparating wall and to the entrant surface of said workpiece; a cylinderin said hub portion communicating with said second chamber; anadjustable piston disposed in said cylinder; and means for adjusting therelative position of said piston in said cylinder.